On Windows 10, I run
dism /online /import-defaultappassociations:\\path\to\appassociations.xml
The output says the command was completed successfully, but the defaults aren't changed when opening files. The changes are also not visible in Control Panel > Default Programs
.
I know the xml is accessible and this command worked on 8.1 computers in our environment. But every Windows 10 computer has had the same issue.
The DISM logs show some warnings, but I cannot really tell if they are related. I can provide them if necessary.